The British government has determined that it is “highly likely” that Russia was behind an assassination attempt against a former Russian spy in England earlier in March.

British Prime Minister Theresa May said in a speech at the House of Commons that a nerve agent used against former Russian military intelligence official Sergei Skripal and his daughter has been positively identified and has been used by the Russian government in the past.

“Based on the positive identification of this chemical agent by world leading experts…knowledge that Russia has previously produced this agent and would still be capable of doing so, Russia’s record of conducting state-sponsored assassinations, and our assessment that Russia views some defectors as legitimate targets for assassinations, the government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal,” said May. (RELATED: UK Specialists Examine Skripal Attack)

May said that the “military-grade” nerve agent that was used is part of a substance developed by Russia known as “Novichok.”

May said that evidence gathered so far points to “only two plausible explanations.”

“Either this was a direct act by the Russian state against our country, or the Russian government lost control of its potentially catastrophically damaging nerve agent and allowed it to get into the hands of others,” she said.

May also said in her speech that the government has summoned Russia’s ambassador to account for how the nerve agent “could have been deployed in Salisbury against Mr Skripal and his daughter.”

The ambassador “must immediately provide full and complete disclosure” of the “Novichok” program, she said.

Skripal has lived in England since 2010 after he was released from a Russian prison as part of a prisoner swap for 10 Kremlin spies who were in FBI custody.

Skripal was originally sentenced to 13 years in prison in 2006 after he was convicted of selling secrets to British intelligence.

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